Electromagnetic instrument.



Patnted Nov.14, 1911.

ELEGTBOMAGNBTIG INSTRUMENT.

APPLICATION rILnn 001.26, 1910.

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BO scale by means of UNITED sTATEs PATENTQ; y

WALTER K. MENNS, 0F MALDEN, MASSACHUSETTS, ASSIGNB lO CHARLES H.PEARSON, 0F BROOKLINE, MASSACHUSETTS.

Specification of Letters Patent.

Patenti ld'Nov. 14, 1911.

Application led otober 26, 1910. Serial No. 589,190.

To all whom it may concern.'

Be it known that LWALTER K. MENNs, a subject of King George V ofEngland, residing at Malden, in the county o Middlesex and State ofMassachusetts, have i-n vented new and useful Improvements inElectromagnetic Instruments, of which the following 1s a specification.

This invention relates to improvements in indicating devices such aselectricity meters, tachometers and electro-magnetic speed indicators,and particularly to electro-magnetic indicating devices of that class inwhich the indicating element is moved by a disk of low electricalresistance placed within the field of a 'magnetic rotor which, when rotated, sets up lines of magnetic force Howing through the disk producinga braking effect which tends to rotate the disk with the rotor, therebeing provided a spring restraining the disk and acting to return it toits initial or zero position when the magnetic rotor ceases to rotate.The variable rotation of the magnetic 'rotor due to the variable speedof the machine to which it is lconnected to be driven acts to move theindicating element to varying positions corresponding to the speed o themachine, there being provided a suitable graduated which theV speed maybe read. Such instruments have been found to be very seriously affectedin their accuracy by variations in temperature as, for example, in thecase of magnetic speedometers for automobiles which areusually'calibrated at a temperature of about 68 or 70 F., actual testshave shown an inaccuracy in reading amounting to 16% over-registrationat 16.3 F. and amounting to 15% under-registration at 137 .5 F., thevariation per degree change of temperature being .27 This means adiscrepancy'of about ten miles er hour between summer and winterreadings when actually travelin at sixty miles per hour, and adiscrepancy o about ve miles per hour when actually traveling at thirtymiles, per hour. Since the readmg ofl the instrument is proportional tothe currents induced in the pivoted disk by the rotating magnet and thecurrents are inversely 4proportional to the electrical resistance of thedisk, the variations in temperature must seriousl affect thespeedometerreadings.

4It is a act that the magnetism of the rotating magnet decreases as thetemperature increases from normal, thu t is', 70o F., and innormal, andas ,the tortue on the disk deendsupon the square if the magnetic fieldintensity, the variation i1 i the strength o the magnet means double thevariation in the speedometer reading. lleretofore, attempts have beenmade in lvaiious ways to over come 'these inaccuracies, but thus far theand delicate to be prac ical and have been uncertain and inaccuratl intheir results.

The object cf my inv antion is to provide a simple, inexpensive an dreliable means for lcompensating for chan ges of temperature by changingthe relativ: location of the rotating magnetand pivo ed disk, or therelamember, or the relativelocation of the mag- To these ends, myiivention consists in the novel features of :onstruction and in thecombination and a: rangement of parts set forth in the following seciticaton and particularly poinhted oui in tlie claims.

Referring to the dra` vings: Figure 1 is a plan of an electro-magneticindicating instrument embodying in] invention, the cover being removed.Fig. S is a sectional view Itaken on line 2-2 of Fig. 1f Fig. 3 is a-plan of a modilicatiol of the instrument there are a plurality ofthermostats while vin Fig. 3, there is a Asi lgle tubular thermostatsurrounding the ina net and indicating parts. Fig. 4 is a v`articalsectional view of another type of el( ctromagnetic instrumentembodying m in vention.

Like numerals re er 1 o like parts throughout the several views o thedrawings.

and 3, wherein I have shown an electromagnetic speedometer of the Warnertype, and referring n( w more particularly to Figs. 1 and 2,5 is tlieouter casing, 6 the magnetic rotor carriel by a hollow cupshapedmember 6', 7 tl le ield ring, and 8 1s the aluminum disk in .erposedbetween the magnetic rotor and. tl le field member and aiiixed toa'shaft 9 'pir oted in b'rins consisting of screw-threacl ed rods 10 an11 so as to swing freely on tl the rotor 6 rotates. '..his disk, whichcarries the 'indicating element, is,provided with means employed havebeen too expensive tive locatlon of the m tgnet and the 'field' net, thepivoted disk a1 d thejeld member,V

In the drawings, re erring to Figs. 1, 2

le same axis on whichcreases as the temperat ire decreases below shown1n Figs. land 2 an d differing therefrom in that in the form' shc wn inFigs. 1 and 2,

This spring a vertical fiange 12 which, in practice, is provided withsuitable numerals on its periphery, not shown, which numerals are viewedt rough a window 13 in the casing 5. The bearings 10 and 11 and thefield ring 7 are mounted in an inner casing 14 which is of non-ferrousmaterial. When the rotor 6 is rotated, it generates eddy currents in themetal disk 8, the reaction of these currents .on the magnetic field ofthe rotor supplying a tor ue to the disk, so that the magnetic pull tereon tends to rotate the disk with the rotor. The disk, however, isrestrained by suitable means consisting of a hair spring 15 secured atits inner coil to the shaft 9 and at its outer end to a suitable fixedpin 16. acts to keep the indicator steady at all spee s and return it tozero when the magnetic rotor 6 stops. The field ring 7 serves toconcentrate and conserve the magnetism, thereby insuring a more powerfulpull onthe pivoted disk 8. Thus far, the construction and operation areWell known to those skilled in the art.

I will now proceed to described the means whereby I am enabled tocompensate for changes in temperature, whereby4 the inaccu* racies ofthe instrument owing to variations of temperature are obviated. Theinner casing 14 which contains the field ring 7 and the pivoted di'sk 8is supported by one or more thermostats, each of which com irises a bodycomposed of hard rubber which is employed because it'has a very highcoefficient of expansion. In Fig. 2, I have shown .two of these hardrubber thermostat-s 17 and 18 which may be segmentalxin form, and inFig. 3, I have shown a single thermostat 19 which is annular in form andsurrounds the magnetic rotor and the indicatingparts.

he thermostats 17 and 18 constitute supporting posts for` the innercasing 14 to which they are connected by suitable means such, forexample, as brackets 20 and 21 secured to the lower extremities of saidposts, respectively, while the upper extremities of said pbsts aresupported, respectively,

by plates 22 and 23 secured to the outer cas-` ing 5.v The len tli ofthese lposts is such v that at a norma temperature, say 70 F.,

at which 'the instrument is graduated, the

air gap between the magnetic rotor Gand' the aluminum disk 8 is suchthat the readling ofthe instrument is correct for' all eeds and whenthe4 temperature varies a ove and below normal, the thermostats 17 and18 expand and contract `vertically, thus raisin and lowering the casin14 together with t e ring 7 and disk 8, it eing understood Vthat whenthe temperature goes bellow normal the casing is raised and when thetemperature goes above normal the cas- ;inis lowered.

ince the magnetism of the rotating inag- Ipivot .nearer to the magneticrotor 25.

net decreases as the temperature increases, and increases as thetemperature decreases, it will be seen that by makingthe thermostats 17anl 18 the proper length these changes of temperature can be compensatedfor by imparting to the disk 8 or the ring 7 or both a motion relativeto the rotating magnet 6, thus varying the gap between the rotatingmagnet and the disk 8 and ring 7. Consequently, although the'iield ofthe rotating magnet varies -in intensity according to changes oftemperature, the torque upon the pivoted disk 8 is made uniform by theemployment of these thermostats and the readings of the instrument aremade substantially correct for all speeds,

Referring now to Fig. 4, wherein I have shown What is well known tothose in the art as the Stewart type of electro'- magnetic speedometer,24 is the casing in which is journaled the magnetic rotor 2 5 and placedabove this rotor is a metallic disk 26 of low electrical resistancemounted upon a shaft 27. Above this disk is located a field disk 28which serves to concentrate and conserve the magnetism of the magneticrotor, thus insurin a very powerful pull on the pivoted dis 26. Theshaft 2 7 is journaled in a bearing 29 in which it is capable of slidingfreely vertically ,andl is journaled at 'its' lower end in a pivotbearing 30. The upper end of the shaft carries an indicator hand 31. Ahair spring '32 which is aiiixed at its inner coil to the shaft 27 andat its outer end to aA fixed pin 33 tends to resist the rotation of thedisk 2 7 under the influence of the magnetic rotor 25 and acts to returnthe hand 31 to zero position when the rotation of the rotor ceases. Inthis typevof instrument, as in the type first described, the accuracy ofthe instrument is greatly impaired by variations in temperature wh'chcauses a weakening ofthe magnetic force ofthe rotor as the tem eratureincreases and a strengthening of t e magnetic force as the temperaturedecreases. To compensate for these changes, I have sup orted the lowerpivot bearing 30- of the shaft 27 upon the freeend of an arm 34, saidarm being rigidly supported at its other end upon a hard rubber post 35constituting a thermostat, the u per end of this post being suitablysecured to the casing v24. The inner end of the arm 34 projects throughan aperture 36 provided in a hollow shaft 37 constituting a support forthe bearings of the magnetic rotor -25 and constituting lso a guide forthe vertically movable bearing 30. When the temperature rises abovenormal, the hard rubber ost 35 will expand, thus causing the pivotcaring 30 to be 'lowered and carrying the disk 36 0n the other hand,when the temperature falls below normal, the thermostat 35 contracts,

skilled for all and all temperatures.

It w' be understood that both in the' specification and in the claimswhere I have referred to hard rubber thermostats, this term means athermostat composed of a sufficient quantity of hard rubber to give lthenecessary expansive movement to compensati"""for"`changes\ oftemperature. Having thus described my invention, what D I claimanddesire by Letters Patent to secure is: 4

1. An electro-magnetic instrument'having, in combination, means forproducing a ma 5 ed 1n said field, and a thermostat for changin therelative location of said disk and said field to complensate for changesof temperature, said t ermostat consisting of a odycontaining hard `0 2.An'electro-magnetic instrument having, in combination, means forproducing a magnetic field, ametal disk rotatably mountedin said field,and a thermostat for changn. in the relative location of said disk anirubber.

erature, said t ermostat consisting of a ody composed of hard rubber.'

3. An electro-magnetic instrument having, in combination, a eld memberand a coperating rotatable magnet for producing a magnetic eld, a metaldisk rotatably mounted in said field, and means including a hard rubberthermostat forming an opera-` tive connection between said magnet andsaid disk for chan 'n the relative location of said disk and said eld tocompensate for `changes of temperature.y

4. An .electro-magnetic instrument having, in combin ti'on, a fieldmember and a coperating rotatable magnet forproducing a magnetic field,a metal disk rotatably mountedin said field, and means including a hardrubber thermostat f ormin an operative connection between said fie dmembery 55 and saidlmagnet for changing the relative location of saidfield member and said magpet to compensate for changes of temperaure.

' 5. An.l electro-magnetic instrument having, in combination, a fieldmember and a eoperating rotatable magnet for producing a magnetic field,a metal disk rotatably mounted in said field, and means including a hardrubber` thermostat forming an operative connection between said magnetand yof the instrument are substantially ycorrect etic field a metaldisk rotatably mount-` said eld to complensate for changes of tem-4 '8f1- p l i w d 4 l, Lsaid field mmnber and' disk, for changin therelative location of sai1\, field member -and disk to said magnet ltocompensate-iw changes of temperature. y f

6. An electro-magnetic instrument having, in combination, means`including a rotatable magnet for producing a magnetic field, a metaldisk rotatably mounted in said field, and means includ .ng a hard rubberthermostat extending lo ndgltudinally of the axis of said magnet and iskand forming an operative connectio 1 between said magnet and said diskfor ch inging the relative location of said disk and said iield t0compensate for changes of'temperature.

,7. An electro-magnetic` instrument hav'- ing, in combination, a casinga field member .and a cooperating rotatable magnet located in said casinor produc mg a magnetic field, a metal isk rotatably mounted in saideld, a hard rubber thermos 1at for changing the relative location ofsai( disk and magnet to compensate for 'char ges of temperature, saidthermostat being secured at one end to said`casin and meals connectinthe other end of sai thermosta .,to said dis 8. An electro-magneticinstrument having, in combination, an out: r casing, a magnet rotatablymounted in said casing for producing a magnetic field, an inner casingocated withinI said outer casing,- a meta disk rotatably mounted in Maidinner casing in said field, and a 4hard r lbber thermostat secured atone end to said `)uter cas` and havingits other end conne( ted to saidmner '100 casing for changingthe re ative location of t said disk andmagnet to compensate for "changes of temperature.

9. An electro-magnetic instrument havmostatic device, whe y tl erelation of said l `member with respect to th s rotating field is variedaccording to .vari: ,tions in atmosheric temperature, to v ry the linesof y orce el'ective to rotate sa 1.d member.'

10. An .electro-magnetic instrument have ing, in combination, means forcreating a' rotating magnetic field, a member arranged within theiniiuence of sa 'Ld field to beroing said rotation, and a ha fd rubbermember operated by variations in. atmospheric temperatu're for movingsaid. first-named memer in said field to vary tl e number of lines i offorce of said field cut b v said member. 12|

11. An electromagneti instrument having, in combination, mea ns forcreating a rotating magneticeld, a member arranged within the influenceof s: `id eld to be rotated thereby, a spindle o1, which said mem- 13ing, in combination, means for creating a tated thereby, means foryieldingly opposl yber is supported, means connected to said spindle foryieldingly opposing said rotation, and means for supporting said spindleincluding a hard rubber thermostatic device whereby the relation of saidmember with reference to the rotating field is varied according tovariations in Aatmospheric tem- 'ment of the magnet and magnetic mass toperature, -to vary the number of lines of lf)orce of the rotating fieldcut by said memer.` s Y 12. An electro-magnetic instrument having, incombination, a magnet and a magnetic mass, a member'arranged to extendinto-the space` between said mass and said magnet, means forcausingrelative movecreate a rotatingv magnetic field in said space, and meansto form a support for said member including a hardrubber member.

13; An electro-magnetic instrument having, in combination, a ma neticmass, a hollow rotata le support carrying one of "these parts, arodlongitudiet and a magnally movable within said supipor', means forsupporting said vrod inclu ing a hardrubber thermostatic device, and amember carried by vsaid rod, said member being interposed between saidmass and said magnet..

`14a An electro-magnetic instrument having, in combination, a magnet anda magnetic mass, a hollow rotatable support for one of'y these parts, arod longitudinally -movable within said support, a member interposedbetween` said ma t and said mass, a spindle upon which said member ismount.

ed, said spindle being supported on said rod, l

